Actually, it was my understanding that 480i is standard tv, and that 480p 720p, and 1080i are *all* HD signals. Typically (at least with my stuff), you need to set the TV to the HD signal you'll be sending it, as well as setting the DVD player to the signal you'll be sending. Also, even though a player may upsample, not all signals can be sent by the same connections: theoretically, my TV is 1080i compatible and my DVD player will send a 720p or 1080i signal-but only over the DVI-D or HDMI link...and my TV has no higher resolution connection than component. Consequently, I watch movies at 480p (which is still much better than the regular signal).
So to answer your question (finally): 480p is HD and your tv supports it-good for you; but unless your TV upsamples that signal to 720p or 1080i thats the best you're going to get without buying a new DVD player.
BRyan...sorry 'bout that...